A dental instrument holder is a device that holds dental instruments within a dental operating theater, providing dental personnel with convenient access to those instruments. A dental instrument holder is usually mounted on an elongated rod, which may extend from a control unit or mechanical arm system. The elongated rod fits within a cylindrical cavity in the instrument holder and is usually secured within the cavity by a setscrew, which impinges upon the rod through a threaded setscrew hole in the holder.
The holder can be rotated slightly about the rod so that the user can select an orientation of the holder that provides the most convenient angle for holding the instruments. To provide for manual rotation adjustment for the instrument holder, a friction pad is provided between the setscrew and rod. The pad is pressed by the screw against the rod. The friction between the pad and rod provides a smooth resistance to instrument holder rotation. The amount of the resistance is adjustable by tightening or loosening the setscrew.
With the increased use of plastics in dental equipment holders, some disadvantages in the just-described system have become apparent. Notably, the high torques commonly applied to the setscrew when mounting the holder to the rod can cause compression cracks to form in the plastic adjacent to the threads of the setscrew.
The compression cracking occurs because the highly torqued setscrew causes significant permanent stresses in the plastic surrounding the setscrew. These stresses alone may be enough to cause compression fracture. Alternatively, the plastic may be permanently stressed so close to fracture that cracks can initiate from the minor impacts repeatedly sustained by the instrument holder as the instruments are removed and inserted.
In light of the disadvantages in the prior art, one objective of the present invention is to provide a rotation adjustment mechanism for a dental instrument holder, which mechanism does not cause compression fractures in the instrument holder.
A rotation adjustment for a dental instrument holder, in accordance with one aspect of the present invention, avoids the creation of harmful stresses in the plastic holder as a result of setscrew torquing. The subject invention includes a dental instrument holder with a cylindrical cavity that receives an end of an elongated rod. A setscrew hole is transversely located through the end of the rod. A setscrew is threaded in the hole. The end of the screw protrudes against the cavity wall to provide resistance to rotation of the instrument holder about the rod. The setscrew is accessed by a tool, such as an Allen wrench, through an access opening in the instrument holder. Because the setscrew is threaded within the rod, which is usually metallic, the above-described compression cracks in the holder are eliminated.